The early detection of breast cancer has been shown to significantly improve patient survival. Present methods of breast cancer detection include screening mammography and palpation, either by patient self-examination or clinical breast exam. Palpation relies on the manual detection of differences in tissue stiffness between breast lesions and normal breast tissue. The success of palpation is due to the fact that the elastic modulus (or Young's modulus) of malignant tumors is often an order of magnitude greater than that of normal breast tissue. That is, cancerous lesions feel “hard” or “stiff” as compared to normal breast tissue. See T. Krouskop et al., Ultrasonic Imaging 20, 260-274 (1998); A. Saravazyan et al., Acoustic Imaging 21, 223-240 (1995).
Recently, the use of ultrasonic radiation force to remotely characerize tissue stiffness has been proposed. One particular approach is referred to as remote palpation. In remote palpation, acoustic radiation force is used to apply localized forces within tissue, and the resulting tissue displacements are mapped using either ultrasonic correlation based methods, or other pattern matching methods. A volume of tissue that is stiffer than the surrounding medium (i.e., a lesion) may distribute the force throughout the tissue beneath it, resulting in larger regions of displacement, and smaller maximum displacements. Remote palpation is described in K. Nightingale, Ultrasonic Generation and Detection of Acoustic Streaming to Differentiate Between Fluid-Filled and Solid Lesions in the Breast (Ph.D. Thesis, Duke University, September 1997), and in K Nightingale et al., Proceedings of the 1997 IEEE Ultrasonics Symposium, 1419-1422 (Toronto, Calif., October 1997).
U.S. Pat. No. 5,921,928 to Greenleaf uses sound and sonic waves to vibrate tissue and monitors the sound of the vibrating tissue. A disadvantage of such am approach is that different transmit and detection systems may be required, and multiple pushing cycles at a single location may be required.
Remote palpation has not yet been implemented in a form feasible for actual clinical diagnosis. Accordingly, there remains a need for new methods and systems to implement remote palpation.